title: Kinematic analysis of the backstroke start: differences between backstroke specialists and non-specialists.
abstract: The purpose of this study was to clarify factors to perform the hole-entry technique in the backstroke start. A total of 16 well-trained Japanese competitive swimmers were divided into two groups (backstroke specialists and non-specialists) to compare their backstroke start motions. Their backstroke motions were videotaped, and two-dimensional co-ordinates for the swimmers were obtained from the video images using direct linear transformation methods. A non-paired t-test and Mann-Whitney U-test were used to analyse the statistical difference of the kinematic variables between the groups. Backstroke specialists showed a significantly shorter 5 m time (P = 0.009, effect size = -1.54), a significantly higher position of the toe (P = 0.010, effect size = 1.47) at signal and of the hip at toe-off (P = 0.002, effect size = 1.94), a significantly larger hip joint angle at toe-off (P = 0.007, effect size = 1.60) and a significantly higher angular velocities of the hip joints (45-85%; P < 0.05) for the normalised time as compared to that of non-specialists. An earlier initiation of the extension and the maintenance of a higher extension speed at the hip joints were important factors in achieving an arched-back posture, which facilitated and water entrance with a small entry range.
authors.affiliation: a School of Sport Sciences , Waseda University , Tokorozawa , Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Takeda
authors.forename: Osamu
authors.initials: O
authors.lastname: Itoi
authors.forename: Hideki
authors.initials: H
authors.lastname: Takagi
authors.forename: Shozo
authors.initials: S
authors.lastname: Tsubakimoto
mesh_terms: D000328:Adult; D056352:Athletes; D054874:Athletic Performance; D001696:Biomechanical Phenomena; D005260:Female; D006615:Hip; D006621:Hip Joint; D006801:Humans; D007564:Japan; D008297:Male; D011361:Professional Competence; D016059:Range of Motion, Articular; D013550:Swimming; D013647:Task Performance and Analysis; D014034:Toes; D055815:Young Adult